Humans are a puzzling species. On the one hand, we struggle to survive on our own in the wild, often unable to solve basic problems, like obtaining food, building shelters or avoiding predators. On the other hand, human groups have produced innovative technologies, sophisticated languages, and complex institutions that have permitted us to successfully expand into environments across the globe. What has enabled us to dominate such a vast range of environments, more than any other species? The Secret of Our Success lies not in our innate intelligence, but in our collective brains—in the ability of human groups to socially interconnect and to learn from one another.

Drawing insights from lost European explorers, clever chimpanzees, hunter-gatherers, neuroscientists, ancient bones, and the human genome, Joseph Henrich demonstrates how our collective brains have propelled our species’ genetic evolution, and shaped our biology. Our early capacities for learning from others produced many innovations, such as fire, cooking, water containers, plant knowledge and projectile weapons, which in turn drove the expansion of our brains and altered our physiology, anatomy and psychology in crucial ways. Further on, some collective brains generated and recombined powerful concepts, such as the lever, wheel, screw and writing. Henrich shows how our genetics and biology are inextricably interwoven with cultural evolution, and that this unique culture-gene interaction has propelled our species on a unique evolutionary trajectory.

Tracking clues from our ancient past to the present, The Secret of Our Success explores how our cultural and social natures produce a collective intelligence that explains both our species striking uniqueness and odd peculiarities.

Questions about the origins of human cooperation have long puzzled and divided scientists. Social norms that foster fair-minded behavior, altruism and collective action undergird the foundations of large-scale human societies, but we know little about how these norms develop or spread, or why the intensity and breadth of human cooperation varies among different populations. What is the connection between social norms that encourage fair dealing and economic growth? How are these social norms related to the emergence of centralized institutions? Informed by a pioneering set of cross-cultural data, Experimenting with Social Norms advances our understanding of the evolution of human cooperation and the expansion of complex societies.

Editors Jean Ensminger and Joseph Henrich present evidence from an exciting collaboration between anthropologists and economists. Using experimental economics games, researchers examined levels of fairness, cooperation, and norms for punishing those who violate expectations of equality across a diverse swath of societies, from hunter-gatherers in Tanzania to a small town in rural Missouri. These experiments tested individuals’ willingness to conduct mutually beneficial transactions with strangers that reap rewards only at the expense of taking a risk on the cooperation of others. The results show a robust relationship between exposure to market economies and social norms that benefit the group over narrow economic self-interest. Levels of fairness and generosity are generally higher among individuals in communities with more integrated markets. Religion also plays a powerful role. Individuals practicing either Islam or Christianity exhibited a stronger sense of fairness, possibly because religions with high moralizing deities, equipped with ample powers to reward and punish, encourage greater prosociality. The size of the settlement also had an impact. People in larger communities were more willing to punish unfairness compared to those in smaller societies. Taken together, the volume supports the hypothesis that social norms evolved over thousands of years to allow strangers in more complex and large settlements to coexist, trade and prosper.

Innovative and ambitious, Experimenting with Social Norms synthesizes an unprecedented analysis of social behavior from an immense range of human societies. The fifteen case studies analyzed in this volume, which include field experiments in Africa, South America, New Guinea, Siberia and the United States, are available for free download on the Foundation’s website.

Human populations differ reliably in the degree to which people favor family, friends, and community members over strangers and outsiders. In the last decade, researchers have begun to propose several economic and evolutionary hypotheses for these cross-population differences in parochialism. In this paper, we outline major current theories and review recent attempts to test them. We also discuss the key methodological challenges in assessing these diverse economic and evolutionary theories for cross-population differences in parochialism.

The sanctioning of norm-transgressors is a necessary-though often costly-task for maintaining a well-functioning society. Prior to effective and reliable secular institutions for punishment, large-scale societies depended on individuals engaging in 'altruistic punishment'-bearing the costs of punishment individually, for the benefit of society. Evolutionary approaches to religion suggest that beliefs in powerful, moralizing Gods, who can distribute rewards and punishments, emerged as a way to augment earthly punishment in large societies that could not effectively monitor norm violations. In five studies, we investigate whether such beliefs in God can replace people's motivation to engage in altruistic punishment, and their support for state-sponsored punishment. Results show that, although religiosity generally predicts higher levels of punishment, the specific belief in powerful, intervening Gods reduces altruistic punishment and support for state-sponsored punishment. Moreover, these effects are specifically owing to differences in people's perceptions that humans are responsible for punishing wrongdoers.